This invention relates to an infrared transmitting optical wave guide, and more particularly to an infrared transmitting optical wave guide useful for the transmission of infrared having a wavelength of 2 to 6 microns.
Measurement of low temperature close to room temperature generally demands the use of a material which allows permeation of an infrared having as long a wavelength as possible. Where temperature measurement is made in an extremely narrow area or where a temperature gauge can not be brought near the object for measurement, then it is necessary to provide a means to measure temperature by transmitting infrared to a place remote from the object.
In recent years, zirconium fluoride glass is regarded as useful as a material of optical wave guides which allows the passage of infrared having such a long wavelength as 2 to 6 microns. An optical wave guide is recently proposed which is formed of the above-mentioned type of glass. However, the zirconium fluoride glass is thermally unstable and presents a problem of being crystallized by heat. Moreover, the zirconium fluoride glass has a narrow glass-forming region, making it impossible to produce glass materials having widely varied compositions. Consequently, it is difficult to obtain glass materials having different refractive indices. To date, therefore, there has been no infrared transmitting optical wave guide whose core and cladding are both made of zirconium fluoride glass. As a solution to the above-mentioned problem, it is proposed to dope the core glass component with a composition capable of increasing the refractive index of the glass, for example, lead fluoride, or bismuth fluoride. However, addition of such composition harms the stability of the zirconium fluoride glass. Therefore, no success has been achieved yet by such method.